The present invention relates to a process for preparing polyglycerol fatty acid ester mixtures from a C.sub.8 - to C.sub.24 -fatty acid and a polyglycerol mixture containing 0 to 5% by weight of monoglycerol, 15 to 40% by weight of diglycerol, 30 to 55% by weight of triglycerol, 10 to 25% by weight of tetraglycerol and 0 to 30% by weight of higher polyglycerols with acidic catalysis.
The invention furthermore relates to polyglycerol fatty acid ester mixtures, thickening agents and oil/water emulsifiers prepared by the process and having a very specific composition with respect to the polyglycerol employed, the fatty acids used and the degree of esterification, and to the use of pclyglycerol fatty acid ester mixtures of this type.
The main industrial production of polyglycerol fatty acid ester mixtures is based on the direct esterification of fatty acids with polyglycerols of various chain lengths which are designated as a polyglycerol mixture or simply as polyglycerol) in the presence of an alkaline catalyst at elevated temperature. The known processes, however, are not selective, so that mixtures of undefined esters of polyglycerols with saturated and unsaturated fatty acids are obtained. The preparation of polyglycerol fatty acid esters of defined composition necessitates a complicated reaction sequence (in general introduction of protective groups into the polyglycerol compounds is necessary), and the reaction conditions are difficult to control.
The use of mixtures of polyglycerol fatty acid esters as emulsifiers in cosmetic and pharmaceutical preparations is disclosed in Published German Patent Application No. DE 4,005,819, the polyglycerol fatty acid ester mixture being prepared by partial esterification of polyglycerol mixtures of 0 to 5% by weight of monoglycerol, 15 to 40% by weight of diglycerol, 30 to 55% by weight of triglycerol, 10 to 25% by weight of tetraglycerol and 0 to 30% by weight of higher polyglycerols with at least one unsaturated fatty acid having 16 to 22 carbon atoms. Partial esterification of the polyglycerols occurs, but only an undefined mixture of polyglycerol fatty acid esters having a general degree of esterification of between 20 and 70% is obtained. The teachings of this document do not enable preparation of polyglycerol fatty acid ester mixtures having a specific composition and distribution of the esters in the mixture.
Published German Patent Application No. DE 3,902,374 discloses a detergent, cleaning agent and/or body shampoo which, in addition to an ionic and/or amphoteric surfactant, contains C.sub.8 to C.sub.18 fatty acid monoesters of diglycerol and/or C.sub.8 to C.sub.18 fatty acid diesters of tetraglycerol. This composition is characterized by good processability and skin compatibility and is readily biodegradable. However, it has the disadvantage that a relatively expensive and energy-consuming multi-step process is required for its preparation. It also has the disadvantage that it is normally obtained as a solid product, which leads to difficulties during further processing, e.g. into preparations etc., because it cannot be pumped at room temperature. There is also a risk of blockage of supply and metering devices. To dissolve the product it is necessary to apply heat and/or strong shear forces.
European Patent Application No. EP-A 0,289,636 discloses an emulsified or solubilized sterol composition in which the sterols are emulsified or solubilized in an aqueous solution of a polyhydroxy compound or in a liquid polyhydroxy compound which contains sucrose and/or polyglycerol fatty acid esters. The polyglycerol fatty acid esters which act as solubilizers and emulsifiers are obtained by esterification of polyglycerols having a degree of polymerization of 4 to 10 and saturated and/or unsaturated fatty acids containing 10 to 24 carbon atoms, the content of monoesters being at least 50% by weight.
Despite all the activity of the prior art, there remained a need for polyglycerol fatty acid ester mixtures having a defined composition and improved properties and handling and for an economical process for preparing such polyglycerol fatty acid ester mixtures.